1. Field of the Invention
The present invention is broadly concerned with a demand-type pneumatic valve particularly adapted for administering medicinal gas, normally oxygen, to a patient undergoing respiratory therapy. More particularly, it is concerned with a compact, to tally pneumatic demand valve useful in a wide variety of contexts, including hospital, home care and ambulatory settings.
2. Description of the Prior Art
The traditional approach in administration of a medicinal gas such as oxygen is to connect the patient via a cannula to a source of pressurized gas, with the gas being administered on a more or less continuous basis. In the case of oxygen, however, studies have indicated that, in the continuous administration mode, significant quantities of oxygen are lost. That is to say, during the normal breathing cycle, the patient will inhale, exhale and pause before beginning the next inhalation; as a consequence, oxygen delivered to the patient during the exhale and pause portions of the breathing cycle are essentially wasted.
In response to this problem, it has been known in the past to provide valves of the so-called demand type, i.e., valves adapted to open only during the inspiration period of the patient's breathing cycle. Thus, U.S. Pat. No. 4,054,133 to Myers describes a demand-type valve of the pneumatic variety.
The Myers valve makes use of a sensing diaphragm arrangement made up of a pair of interconnected flexible diaphragms which cooperatively define a chamber. An adjustable spring engages one of these diaphragms in an attempt to provide a measure of sensitivity control. Moreover, the Myers device includes a rather complicated arrangement associated with the dual diaphragm structure designed to prevent the wastage of control volumes of gas, which typically may account for only 4 or 5% of the volume of gas used. As a consequence, the Myers design is inherently costly, and is believed prone to malfunction because of the inability to precisely respond to the changing pressure conditions induced during the patient's breathing cycle.
Thus, while the concept of a demand valve is known, there is a real and unsatisfied need in the art for a simplified, low cost, compact pneumatic demand valve.